Heat consumption always happens in electronic products, and the scale of heat consumption of electronic element influences the heat dispersal inside the electronic product. However, since the size of electronic product is getting smaller owing to the technology development, a better heat-dispersing device must be used. Therefore, the design of the control device for the heat-dispensing fan which is installed in the electronic product has become an importance in the industry. Furthermore, because the modern electronic product requests more efficient heat dispersion, the control circuit of the heat-dispersing fan also relatively demands a better efficiency. Thus, the design of the voltage regulating control circuit for the heat-dispensing fan also means a lot in the industry.
The methods for controlling the heat dispersion of the electronic device can be divided into manual-control mode and auto-control mode. References to the manual-control mode are as disclosed in R.O.C. Patent Publication Nos. 527090, 545624 etc., and references to the auto-control mode are as disclosed in R.O.C. Patent Publication No. 420326, R.O.C. Patent Nos. M241884, M250225 etc. However, no matter the auto-control or the manual-control mode, both can be concluded as FIGS. 1 and 2. Currently, the proposed control modes are mainly achieved by utilizing a temperature sensing element, such as thermistor, to constantly detect the temperature coefficient of the environment inside the electronic device as the electronic device is operated, and then changing the driving electricity inputted to the heat-dispersing fan by altering the impedance of the temperature sensing element or altering the wire resistance in the shunt circuit according to the coefficient variation. As shown in FIG. 1, the rotation speed and the temperature have a linear relationship, but this kind of control mode still might cause an unstable voltage supply. Generally, the heat-dispersing fan of a power supplier not only provides the heat-dispersing function for the electronic element inside the power supplier, but also has to exhaust the heat produced by other electronic devices in the computer (such as CPU, hard disk etc.). Therefore, the position of the power supplier and the quantity or position of other electronic devices will influence the direction and temperature of the wind guided by the heat-dispersing fan, the noise caused by wind shearing, and also the efficiency of heat-dispersion. Furthermore, owing to the influence of temperature rising, falling and current variation, the temperature sensing element might have problems of heat consumption and material carbonation which may cause the current hard to control.
Besides, the position of the temperature sensing element and the heat current direction inside the casing are also important. The relationship therebetween may influence the supplied current to the heat-dispersing fan so as to indirectly cause the rotation speed thereof unstable and therefore a rotation noise. Currently, for most computer products, such as personal computer, server computer, or barebone computer, the advantage thereof is quiet as operating. However, if the heat-dispersing fan has an unstable current input or fluctuant power input, the rotation of the fan may be influenced to generate shearing noise; or if the current transiently rises or falls, the rotation speed may have a transient which also causes the noise. Therefore, the voltage control of heat-dispersing fan in the prior art is unstable and still can be improved.